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DEVELOPMENT AND HORMONE ACTION

Interactions between Auxin and Strigolactone in Shoot Branching Control^1,[C],[OA]

University of Queensland, School of Biological Sciences, Australian Research Council Centre of Excellence for Integrative Legume Research, Queensland 4072, Australia (A.H., C.B.); and Department of Biology, University of York, York YO10 5YW, United Kingdom (A.H., P.S., O.L.)

In Arabidopsis (Arabidopsis thaliana), the carotenoid cleavage dioxygenases MORE AXILLARY GROWTH3 (MAX3) and MAX4 act together with MAX1 to produce a strigolactone signaling molecule required for the inhibition of axillary bud outgrowth. We show that both MAX3 and MAX4 transcripts are positively auxin regulated in a manner similar to the orthologous genes from pea (Pisum sativum) and rice (Oryza sativa), supporting evolutionary conservation of this regulation in plants. This regulation is important for branching control because large auxin-related reductions in these transcripts are associated with increased axillary branching. Both transcripts are up-regulated in max mutants, and consistent with max mutants having increased auxin in the polar auxin transport stream, this feedback regulation involves auxin signaling. We suggest that both auxin and strigolactone have the capacity to modulate each other's levels and distribution in a dynamic feedback loop required for the coordinated control of axillary branching.

² These authors contributed equally to the article.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Christine Beveridge (c.beveridge{at}uq.edu.au).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.109.137646

^* Corresponding author; e-mail c.beveridge{at}uq.edu.au.

Received February 24, 2009; accepted July 21, 2009; published July 29, 2009.

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